So far, as electroconductive porous materials, carbon porous bodies and metal oxide porous bodies, which have a aperiodic porous structure, are proposed. Among these, electroconductive oxides such as metal oxide porous bodies, by making use of the electrical characteristics thereof, are at present in wide use as gas sensors and the like. Furthermore, tin oxide (SnO2), indium oxide (ITO) and the like, which are transparent electroconductive oxides, because of the electrical characteristics and optical characteristics thereof, are widely adopted in many fields such as electrodes, selective transmission films and heat reflective films of electronic devices such as solar batteries and EL elements, and electroconductive films for touch panels and the like.
Furthermore, as an oxide having a periodical porous structure, an insulating film that has silica as a skeleton is as well proposed (JP-A No. 2003-17482). The insulating film, having a periodical nanoporous structure, in spite of being high in the porosity, can maintain sufficient mechanical strength; accordingly, it is in wide use as interlayer insulating films of semiconductor devices. In order to achieve high-speed and lower power consumption operation of semiconductor devices, it is very important to make the dielectric constant of the interlayer insulating film lower.
In the case of the aperiodic porous structure, the safety is not sufficient; accordingly, in order to achieve further safety, heat resistance and porosity, various researches are conducted.
Still furthermore, in the former case, since porous structures are formed at random, the mechanical strength is not sufficient; accordingly, when it is used under high temperature in particular, damage tends to be caused and the reliability is deteriorated.
Furthermore, in many cases, the porous structures are not closed. When the porous structure is not closed, the moisture resistance of the film is remarkably deteriorated, resulting in deterioration of the reliability of the semiconductor device.